Catalysts containing metals of Group VIB of the Periodic Table (IUPAC version), especially tungsten and molybdenum and their compounds, especially the oxides or the sulfides exhibit desirable activity in catalyzing a wide variety of reactions including among others, hydrogenation, dehydrogenation, oxidation, desulfurization, isomerization and cracking. Additional metals or their compounds have been combined with the Group VIB metals to provide enhanced catalytic activity. Among the metals utilized in combination with the Group VIB metals are metals of Group VIII of the Periodic Table such as iron, cobalt, nickel and copper or their compounds. Catalysts may be prepared from these mixtures of metals and metal compounds by preparing dilute solutions and applying the diluted solutions to the surface of a foraminous support material. The foraminous support material is usually of a low order of activity when compared to the catalytically active metals or compounds mentioned above, or the support material may be completely inactive catalytically. After the carder is impregnated with the solutions, the impregnated carrier is calcined and/or chemically treated to convert the catalytically active material to other forms and particularly to the oxide. One advantage of this method of preparing catalysts is that the active material present in the solution is evenly distributed over the available surface of the foraminous carrier material.
One of the problems which results when attempts are made to prepare solutions of mixtures of Group VIB and Group VIII metals or metal compounds is the difficulty of preparing solutions and, more particularly, solutions which are stable over a period of time.
U.S. Pat. No. 3,232,887 describes stabilized aqueous catalytically active solutions which comprise an aqueous solvent having dissolved therein catalytically active compounds containing at least one element from Group VIB, at least one element from Group VIII of the Periodic Table, and a stabilizing material which is a water-soluble acidic compound. The water-soluble acidic compound may be a hydroxy monocarboxylic acid, a polyhydroxy monocarboxylic acid, a hydroxy polycarboxylic acid, a polyhydroxy polycarboxylic acid, a monocarboxylic acid, or an oxygenated inorganic phosphorus-containing acid. Among the phosphorus-containing organic acids which are suggested as being useful are hypophosphorus acid, metaphosphorus acid, phosphoric acid, metaphosphoric acid, etc.
Other patents which describe the use of inorganic phosphorus-containing acids in solutions of Group VIB and Group VIII metals or compounds include U.S. Pat. Nos. 3,287,280, 3,755,150, 3,755,196 and 4,818,743. Some of these patents describe the ratio of phosphorus to one or more of the other metals as being an important consideration for improved solubility.